Transcription initiation factor TFIID plays a central role in transcriptional regulation by facilitating promoter responses to various activators. Several reports indicate that TFIID is the direct target for activators and is involved in transducing signals from these activators to other components of the preinitiation complex to facilitate either the assembly or activity of the complex. Although the native TFIID complex can mediate both basal and activator (or repressor)~regulated transcription in reconstituted systems, the TATA box binding subunit of TFIID (TFIIDgamma~TBP) can mediate only basal transcription. Thus, TFIID subunits other than TFIIDgamma must be essential cofactors for regulated transcription. To further understand the functional properties of TFIID and the molecular mechanism of transcriptional regulation, it is important to clone and express each of its subunits and to reconstitute TFIID with the individual factors. TFIID from Drosophila embryo nuclear extracts were purified with anti TFIIDgamma antibody affinity chromatography and seven tightly associated polypeptides (230, 110,85,62,42,28,22 kDa) were identified as candidates for TFIID subunits. To isolate the corresponding cDNAs, partial amino acid sequences of each subunit were determined and used to design oligodeoxynucleotide probes. All TFIID subunits that have been identified have been cloned. Further studies on reconstitution of the recombinant subunits will provide crucial insight into understanding the molecular mechanisms of transcriptional regulation.